Hydraulic Reservoir for Electrohydraulic Actuator

ABSTRACT

An electrohydraulic actuator includes a reservoir tank having a bladder that separates hydraulic fluid from any air in the reservoir tank and includes a sensor system that detects when the hydraulic fluid is depleted from the reservoir tank.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of the filing date of U.S.Provisional Patent Application Ser. No. 62/263,253, filed Dec. 4, 2015,the disclosure of which is incorporated herein by reference

TECHNICAL FIELD

This invention relates to reservoir tanks for hydraulic components andhas particular application to reservoir tanks that can provide make-upor differential fluid required for use in a single rod electrohydraulicactuator units where there is a need for a reservoir to provide extrafluid for the extend stroke and space for excess fluid from the retractstroke.

BACKGROUND

In current hydraulic systems, volumetric changes are common resultingfrom moving parts in the system and temperature changes in the hydraulicfluid. To account for these volumetric changes, current hydraulicsystems include a reservoir tank to contain the overflow that occurs asa result of changes in the volume of the fluid. In any hydraulic system,it is important to prevent the ingestion of air into the system. Inhydraulic reservoirs that are stationary, it is customary to ensure thatthe hydraulic fluid inlet is positioned at the top of the reservoir tankand exit from the bottom of the tank. Because the reservoir tank doesnot move, as long as the fluid outlet port is covered by hydraulicfluid, there is little risk of exposing the outlet port to theatmosphere. In non-stationary applications or in limited spaceapplications, the reservoir tank may not always be in a positionallowing gravity to ensure that the outlet port of the reservoir tank iscovered by hydraulic fluid. Current approaches that address this issueinvolve additional structures and processes in an effort to allow thereservoir tank to tolerate movement. These approaches includepressurized systems and bladder-type systems. Pressurized systems mayrequire specialized tools and equipment to depressurize andre-pressurize the system during repair and maintenance resulting inincreased cost, duration, and complexity.

SUMMARY OF THE INVENTION

At least one benefit over the prior art is provided by anelectrohydraulic actuator system comprising: An electrohydraulicactuator system comprising: an electric motor; a pump; a hydraulic fluidreservoir having a bladder positioned therein, the bladder forming amovable barrier between a hydraulic fluid on one side of the bladder andair on a second side of the bladder and the second side of the bladderfluidly connected to atmosphere outside of the hydraulic fluidreservoir.

At least one benefit over the prior art is provided by anelectrohydraulic actuator system comprising: an electric motor; areversible hydraulic pump attached to and driven by the electric motor;a double-acting, single-rod hydraulic actuator fluidly connected to thehydraulic pump; a hydraulic fluid reservoir attached to the hydraulicpump and fluidly connected to the hydraulic pump, the hydraulic fluidreservoir providing a storage volume for hydraulic fluid that is pumpedinto and out of the hydraulic fluid reservoir; the hydraulic fluidreservoir including a reservoir container including a bladder positionedtherein, the bladder forming a movable barrier between hydraulic fluidon a first side of the bladder and air on a second side of the bladder;the reservoir container having a vent fluidly connecting the second sideof the bladder to atmosphere outside of the hydraulic fluid reservoir,wherein the bladder expands with the intake of air when hydraulic fluidis pumped from the reservoir container and wherein the bladder contractsby allowing the air to leave the reservoir container when hydraulicfluid is pumped into the reservoir container.

At least one benefit over the prior art is provided by anelectrohydraulic actuator system comprising: an electric motor; ahydraulic pump attached to and driven by the electric motor; a hydraulicactuator fluidly connected to the hydraulic pump; a hydraulic fluidreservoir attached to the hydraulic pump and fluidly connected to thehydraulic pump, the hydraulic fluid reservoir providing a storage volumefor hydraulic fluid that is pumped into and out of the hydraulic fluidreservoir; the hydraulic fluid reservoir including a reservoir containerincluding a bladder positioned therein, the bladder forming a movablebarrier between hydraulic fluid contacting an exterior of the bladderand air within the interior of the bladder, the bladder expanding tosubstantially the entire volume of hydraulic fluid exiting the reservoircontainer and contracting by substantially the entire volume of fluidentering the reservoir container; and a sensor system including anelectroactive polymer material bonded to the bladder that provides asignal at least when the bladder has expanded to a predetermined amount.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of this invention will now be described in further detailwith reference to the accompanying drawings, in which:

FIG. 1 is a longitudinal section view of an electrohydraulic actuatorsystem showing the reservoir in an operational condition full ofhydraulic fluid;

FIG. 2 is a longitudinal section view of the electrohydraulic actuatorsystem of FIG. 1 showing the actuator at full extension and showing thereservoir in an intermediate operational condition showing expansion ofthe bladder at normal depletion; and

FIG. 3 is a longitudinal section view of the electrohydraulic actuatorsystem of FIG. 1 showing the actuator at full extension and showingexpansion of the bladder at full depletion (low fluid level).

FIG. 4 is a longitudinal section view of another embodiment of anelectrohydraulic actuator system showing a sealed reservoir in anoperational condition full of hydraulic fluid.

DESCRIPTION OF DRAWINGS

Referring to the FIGS. 1-3, the electrohydraulic actuator system 10comprises an electric motor 12, a hydraulic pump 14, and a hydraulicfluid reservoir assembly 16. The pump 14 is fluidly connected to ahydraulic actuator 18 having an actuator rod 20 retractibly/extendablefrom cylinder 22. The electric motor 12 may be a brushed and brushlesspermanent magnet motor, a stepper motor, or other motor known in the artas appropriate for use in electrohydraulic actuators. The pump 14 istypically a reversible hydraulic pump or other pump known in the art forelectrohydraulic actuators. The pump 14 is reversibly driven by theelectric motor 12 to pump hydraulic fluid to the hydraulic actuator 18as is known in the art. The pump 14 is shown within a cylindrical cover17 and attached to a manifold 15 that houses fluid passageways 9 and isconnected to tubing 11 for fluidly connecting the pump 14 to thehydraulic actuator 18. The hydraulic actuator 18 is shown as adouble-acting, single-rod hydraulic actuator, but is not limited to sucha configuration.

The hydraulic fluid reservoir assembly 16 includes a reservoir chamber25 enclosed by a reservoir shell 26, a first end 28 fluidly connected tothe pump 14 and a second end 30. The second end 30, has a vent 32connecting the interior of the bladder 40 to atmosphere. The reservoirshell 26 may be made of a transparent material. A bladder 40 is shown inthe reservoir chamber 25 which is fluidly connected by vent 30 to theatmosphere outside the reservoir chamber 25. The bladder 40 may be madeof an appropriate elastomeric material. Hydraulic fluid 24 is shown onthe unvented side or exterior of the bladder 40 in the reservoir chamber25. The reservoir chamber 25 includes the volume occupied by thehydraulic fluid 24 and the bladder 40. In FIG. 1, the reservoir chamber25 is shown is a full hydraulic fluid condition with the bladder 40 in asubstantially fully contracted condition which corresponds to a fullyretracted position of the rod 20 of the hydraulic actuator 18.

In FIG. 2, as the hydraulic actuator rod 20 is fully extended, thehydraulic fluid 24 flows out of the hydraulic reservoir chamber 25 andthe bladder 40 expands to substantially the entire volume of hydraulicfluid exiting the reservoir chamber 25. Atmosphere from outside theelectrohydraulic actuator system 10 is pulled through the vent 32 andinto bladder 40.

The electrohydraulic actuator system 10 may further include a sensorsystem 50 which provides a signal when the bladder 40 has expanded to apredetermined amount. The sensor system 50 is shown as a magnet 42 whichis bonded to the bladder 40 and as a low level window 43 tripped with aproximity switch 44. FIG. 2 represents normal depletion of hydraulicfluid from the reservoir chamber 25. In FIG. 3, the electrohydraulicactuator system 10 is shown with the hydraulic fluid in a depletedcondition. The magnet 42 is shown in the low level window 43 trippedwith proximity switch 44. This FIG. 3 represents the maximum depletionof hydraulic fluid 24 from the reservoir chamber 25. This depletioncould be set at 90%, 80%, 70% or any predetermined amount of the volumeof the reservoir chamber 25.

In the reverse operation, and returning sequentially from FIG. 3 to FIG.1, as the piston rod 20 retracts, the hydraulic fluid 24 enters thereservoir chamber 25 and the bladder 40 contracts by substantially theentire volume of fluid entering the reservoir chamber 25. Atmospherefrom bladder 40 is expelled through the vent 32 and to the atmosphere.During operation of the electrohydraulic actuator system 10,substantially no air is in direct contact with the hydraulic fluid 24and the air within the bladder 40 does not contact the hydraulic fluid24.

The shape and construction of the bladder 40 may be tubular in shape andof variable lengths depending upon the application. The bladder 40 isconstructed to allow for a) bonding of a magnet for positionmeasurement, b) visibility of fluid fill when used with clear reservoirshell 26, c) the open end can be cut to length for the particularcapacity required and is suitable for variable sizing/volume, d)sealing/isolation is accommodated by several factors, including thebladder 40 itself as a barrier, capture of the bladder 40 by wrappingover the end of the bladder 40 and past the endcap seal, and the factthat the bladder 40 itself, when pulled in a vacuum, provides additionalsealing as the outer surface of the bladder 40 is expanded against thereservoir shell 26. In addition, the general construction, with inherentisolation, allows for either venting to atmosphere with no risk ofcontamination by using a vent 32, or low pressure pre-load <200 PSI byusing a sealed configuration without a vent 32. The unventedconfiguration is shown in FIG. 4 depicting electrohydraulic actuatorsystem 10′ having hydraulic fluid reservoir assembly 16′ includingsecond end 30′ which does not have a vent. Sealing the reservoirassembly 16′ could result in operational issues due to potential vacuumcreated when hydraulic fluid 24 is removed from the reservoir chamber25, although this may not be a problem in smaller volume units. The useof a sealed reservoir chamber 25 provides the opportunity to induceslight pressure as a means to ensure that hydraulic fluid 24 is forcedinto the operating portion of the electrohydraulic actuator system 10′,so the ability of the reservoir chamber 25 to be pressurized, because itis sealed, provides a benefit to function. Optionally, a sensor 41 madeof an electroactive polymer material can be bonded to the bladder 40′,or formed as at least a portion of the bladder 40′. The sensor 41provides an electric signal to the sensor system 50′ when the bladder40′ expands or contracts.

This present invention has particular application in providing a sealedand/or separated unit that can provide make-up or differential fluidrequired for use in a single rod electrohydraulic actuator unit. Sincethe single-rod electrohydraulic actuator will have differential areas onopposite sides of the piston, there is need for a reservoir to provideextra fluid for the extend stroke and space for excess fluid from theretract stroke. In addition, there is benefit to the tank being able tobe isolated from external contamination (dirt, moisture, aeration, etc.)so that the operating fluid remains clean. A further feature of thecurrent invention is the use of a barrier between the operating fluidand the alternate space that may be sealed or vented, pressurized orsubject to vacuum. The use of this barrier provides the flexibility toincorporate operational features and characteristics that result in avariety of opportunities for usage, as described herein.

Although the principles, embodiments and operation of the presentinvention have been described in detail herein, this is not to beconstrued as being limited to the particular illustrative formsdisclosed. They will thus become apparent to those skilled in the artthat various modifications of the embodiments herein can be made withoutdeparting from the spirit or scope of the invention.

What is claimed is:
 1. An electrohydraulic actuator system comprising:an electric motor; a pump; a hydraulic fluid reservoir having a bladderpositioned therein, the bladder forming a movable barrier between ahydraulic fluid on one side of the bladder and air on a second side ofthe bladder and the second side of the bladder fluidly connected toatmosphere outside of the hydraulic fluid reservoir.
 2. Theelectrohydraulic actuator system as in claim 1, further comprising asensor system that signals when the bladder has expanded to apredetermined amount.
 3. The electrohydraulic actuator system as inclaim 2, the sensor system including a magnet bonded to the bladder. 4.The electrohydraulic actuator system as in claim 2, the sensor systemincluding a proximity switch mounted in the reservoir container.
 5. Theelectrohydraulic actuator system as in claim 2, wherein thepredetermined amount is at least 90% of the volume of the reservoircontainer.
 6. The electrohydraulic actuator system as in claim 2,wherein the predetermined amount is at least 80% of the volume of thereservoir container.
 7. The electrohydraulic actuator system as in claim2, wherein the predetermined amount is at least 70% of the volume of thereservoir container.
 8. The electrohydraulic actuator system as in claim1, further comprising a single rod actuator fluidly attached to thehydraulic fluid reservoir.
 9. The electrohydraulic actuator system as inclaim 1, the hydraulic fluid reservoir including an end cap having anaperture therethrough which fluidly connects the second side of thebladder within the hydraulic fluid reservoir to the atmosphere outsidethe hydraulic fluid reservoir.
 10. The electrohydraulic actuator systemas in claim 1, the hydraulic fluid reservoir including a transparentreservoir shell.
 11. The electrohydraulic actuator system as in claim 1,the bladder being formed at least in part by an electroactive polymermaterial.
 12. The electrohydraulic actuator system as in claim 2, thesignal provided by the sensor system is connected to the Internet. 13.An electrohydraulic actuator system comprising: an electric motor; areversible hydraulic pump attached to and driven by the electric motor;a double-acting, single-rod hydraulic actuator fluidly connected to thehydraulic pump; a hydraulic fluid reservoir attached to the hydraulicpump and fluidly connected to the hydraulic pump, the hydraulic fluidreservoir providing a storage volume for hydraulic fluid that is pumpedinto and out of the hydraulic fluid reservoir; the hydraulic fluidreservoir including a reservoir container including a bladder positionedtherein, the bladder forming a movable barrier between hydraulic fluidon a first side of the bladder and air on a second side of the bladder;the reservoir container having a vent fluidly connecting the second sideof the bladder to atmosphere outside of the hydraulic fluid reservoir,wherein the bladder expands with the intake of air when hydraulic fluidis pumped from the reservoir container and wherein the bladder contractsby allowing the air to leave the reservoir container when hydraulicfluid is pumped into the reservoir container.
 14. The electrohydraulicactuator system as in claim 13, further comprising a sensor system thatprovides a signal when the bladder has expanded to a predeterminedamount.
 15. The electrohydraulic actuator system as in claim 13, thesensor system including a magnet bonded to the bladder.
 16. Theelectrohydraulic actuator system as in claim 13, the sensor systemincluding a proximity switch mounted in the hydraulic fluid reservoir.17. The electrohydraulic actuator system as in claim 14, wherein thepredetermined amount is at least 80% of the volume of the reservoircontainer.
 18. An electrohydraulic actuator system comprising: anelectric motor; a hydraulic pump attached to and driven by the electricmotor; a hydraulic actuator fluidly connected to the hydraulic pump; ahydraulic fluid reservoir attached to the hydraulic pump and fluidlyconnected to the hydraulic pump, the hydraulic fluid reservoir providinga storage volume for hydraulic fluid that is pumped into and out of thehydraulic fluid reservoir; the hydraulic fluid reservoir including areservoir container including a bladder positioned therein, the bladderforming a movable barrier between hydraulic fluid contacting an exteriorof the bladder and air within the interior of the bladder, the bladderexpanding to substantially the entire volume of hydraulic fluid exitingthe reservoir container and contracting by substantially the entirevolume of fluid entering the reservoir container; and a sensor systemincluding an electroactive polymer material bonded to the bladder thatprovides a signal at least when the bladder has expanded to apredetermined amount.
 19. The electrohydraulic actuator system as inclaim 18, wherein the sensor system provides a continuous status of themagnitude of the expansion/contraction of the bladder.
 20. Theelectrohydraulic actuator system as in claim 18, wherein the interior ofthe bladder is fluidly connected to atmosphere outside theelectrohydraulic actuator system by a vent formed through the hydraulicreservoir container.